The manufacturing of ever smaller structures is a constant challenge in the semiconductor industry which uses lithographic processes extensively. The resolution of the lithographic processes is inherently limited by the wavelengths of the illumination source, the mask and the optics used. Currently wavelengths λ of 248 nm and 193 nm are used. Furthermore, illumination sources using shorter wavelengths, such as 157 nm or extreme ultra violet (EUV) sources with 13 nm are being developed. The theoretical resolution limit can be approached on a substrate by a number of techniques that have been developed.
Using special masks like phase shift masks or binary masks with dipole illumination sources a minimal pitch of line structures of 0.25*lambda/NA can be achieved, with NA=numerical aperture of the imaging system. Generally these structures having a smaller critical dimension than the illumination wavelength are called sub-wavelength structures. Patterns with pitches smaller than 0.25*lambda/NA or smaller than the practical minimum pitch that can be achieved with exposure tools are called sub-lithographic, because they must be produced by help of non-lithographic methods like etching and deposition.
To use the potential of the existing illumination sources (e.g. with wavelengths of 193 nm or 248 nm), the manufacturing of fine sublithographic structures, especially fine regular line structures, using spacer techniques has been described e.g. in the DE 42 35 702 A1 and DE 42 36 609 A1.
In DE 42 36 609 A1 a line-by-spacer method is described to produce sublithographic spacers. In US20060024621A1 and DE102004034572A1 a line-by-spacer-fill and a line-by-liner-fill method are described. Line shrink methods are described in the article in Microelectronic Engineering 83, pages 730 to 733.